Hair straightener



FIG. 1 is a perspective view of a hair straightener;

FIG. 2 is a front view thereof;

FIG. 3 is a right side view thereof;

FIG. 4 is a rear view thereof;

FIG. 5 is a left side view thereof;

FIG. 6 is an enlarged top plan view thereof; and,

FIG. 7 is an enlarged bottom view thereof.

The broken lines shown in the drawings illustrate portions of the hair straightener that form no part of the claimed design. 

The ornamental design for a hair straightener, as shown and described above. 